Signaling system



cRoss REFERENCE EXAMINER March 30, 1937. 1. w. CHUBB 2,075,094

' SIGNALING SYSTEM Filed July 26, 1933. 3 Sheets-Sheet 1 RR R u R E' k;U U

March 30, 1937. L. w. CHUBB SIGNALING SYSTEM Filed-July 25, 1933 3Sheets-Sheet 2 INVENTOR law/s May/ii.

'ATTRN Patented Mar. 30, 1937 This invention relates to signaling .andparticularly to means for producing signals at a distance by a beam oflight.

It is an object of this invention to afiord means of communication overa beam of light which will involve no changein the light'which can beobserved without the use of special instruments. In this way secretsignaling can be not visible light.

It is a further object of this invention to use the plane ofpolarization oi plane-polarized light as a means of conveyingintelligence.

It is a further object of my invention to so as- 5 sociate a polarizerat the sending station and an analyzer at the receiving station that theposition of the plane of polarization is at all times indicated at thereceiving station. I

It is a further object of my invention to provide a means for rotatingthe plane of polarization of polarized light in a convenient andemsignaling purposes.

It is a further object of my invention to provide a continuousindication of the position of the plane of polarization of a beam ofpolarized light without requiring an attendant at the receiving stationto manipulate any instrument to discover said position. It is a furtherobject of my invention to provide a photocell so correlated withtheillumination from the above described system that tion will beindicated in the output of the photocell.

It is a further object of my invention'to provide a continuouslyrotating analyzer moving so rapidly that persistence of vision willenable the observer to recognize the direction correspending to theplane oi! polarization.

It is a further object of my invention to proone another in color orother permanent characteristic and each individually polarized in a withthe respective signal to be sent. It is a further object of my inventionto produce an illumination which is crossed by a band of a differentdegree of illumination and to as- 50 so'ciate indicia or othertranslating means therewith, whereby rotation of the band maybeinterpreted as changing the significance of the signal.

5;. the structure proposed will be understood from accomplished,particularly if the light used is cient way, whereby such rotation'maybe used for changes in the position of the plane of polarizaduce aplurality of beams of light diflering from plane which can be rotated atwill in accordance Other'obiects of my inventionfand details,of-

UNITED STATES PATENT OFFICE SIGNALING sis Tm Company, East Pittsburgh,Pa a corporation oi Pennsylvania Application July 26, 1933, Serial N...882.281

18 Claims. (01. 250-415) the following description and the acccmpanyinsI drawings in which:

Figure 1 is an elevational view of one form of the sending device.

Figs. 2 and 3 are diagrammatic views indicat- 5 ing the operation of theapparatus at two diiferent positions.

Fig. 4 is a diagrammatic view of the receiving apparatus partly in sideelevation and partly in section. 10

Fig. 5 is a perspective-view of certain details of the receivingapparatus. I

Fig. 6 is a plan view of the translating means.

7 Fig. 'I is a bottom end view of a portion of a sending apparatusintended for a plurality of 15 simultaneous indications.

- Fig. 8 is a side elevational .view of a larger portion or saidapparatus.

Fig. 9 is a side elevational view of the corresponding receivingapparatus.

Fig. 10 is a section of a photocell of the kind shown in Fig. 9, thesection being on the line x-x of Fig. 13.

Fig. 11 is a diagram 01 the circuits used in connection with saidphotocell. 25

Fig. 12 is a curve to which reference will be -made in explaining theaction of the photocell,

and r e1liig. 13 is a side elevational view of the photoc In Fig. 1 alamp i is shown as representative of any source 0! light. This may bethe light in a lighthouse or a supplemental light, at a lighthouse usedfor this signaling or it may be a beacon independent of any othersignaling sys- 35 tem, if desired. Below it, supported in a frame 2 is asheet of material which will polarize the light passing through it,tourmaline, Iceland spar herapathite, or any similar material may beused. 40 1 The light from the source I is received upon a metal mirror Iwhich is mounted for rotation about a vertical axis. A motor 4 isprovided to drive the rotating mirror, through reduction gearingincluding a worm wheel 5. .The light' A maline or similarm'aterialis'aillxed to the surface II and acts as an, analyser of the polarizedlight. The shape of the body I! is a cylinder cut by two oblique planes,one of which is, is shown in Fig. 5 and is shown in edge view in Fig, 4.

The other oblique plane is shown in edge view' surface, except when itsincidence is nearly normal. When the incidence is nearly normal, thelight will pass through the surface. Light therefore will emerge at theedge II. Fused quartz is suitable for such internal reflection, butother highly refractive materials may be used. It is also possible touse a hollow metal body. but the reflections from the inner surface ofthe metal will be less complete than the internal reflections Justdescribed.

The body If is mounted in a circular support II by means of flanges IIwhich extend to the flat faces I! and II. The frame iI is provided witha crown gear II which meshes with a pinion driven by a motor II.Adjacent the edge iI, at which the light emerges, a ring! is provided,on one face of which, as shown in Fig. 6, indicia are depicted. As shownin Fig. 4, the ring 24 is annular, but if desired, the central portionthereof may be fllled with translucent material or a sheet oftranslucent material may be attached to the ring 24 and cover thecentral portion thereof.

When the translucent material is not used, the

observer looks directly at the brilliant edge II, which, being inmotion, emits a held of light and appears like an illuminated surface,the illumination being distributed as explained below. When thetranslucent material is used, it should be as close to the edge II ofthe body I! as possible to preserve the sharpness of the pattern in thedistribution of illumination.

The indicia need not be compass-direction signs as illustrated in Fig.6, but any sort of characters with any assigned meaning may be used.

In the operation of the system just described the apparatus shown inFig. 1 is mounted in a lighthouse, or at an air port, or at any otherpointwhere regular or frequent sending, of signals indicative ofdirection is desirable. The light from the light source I, passingthrough the polarizer in the frame}, becomes planepolarized light whichis reflected from the mirror I and thrown out as a horizontal beam.

As the mirror. I is rotated by the motor 4, the compass-direction of thehorizontal beam changes progressively. The Beam produced by the act ofreflecting the plane polarized light is' also a beam of polarized lightand as the mirror I rotates the plane of polarization in the horizontalbeam will also rotate about that beam as an axis. This beam will bepolarized in a vertical plane for one position of the mirror I, in ahorizontal plane for a position of the mirror 90 from the first, in avertical plane again for a position of the mirror 180 from the firstposition, etc.

Thus, as the horizontal bcamtakes different :azimuths, in thegeographical sense, it is polarized in different azimuths, in the sensein which.

"azimuth is used in optics. -This rotation of the plane of polarizationof the horizontal beam is a consequence of the polarized char cter ofthe light from the frame I. It can also be called a consequence of themirror I being of metal, although the same polarization in a muchsmaller degree may be observed with a nonmetallic mirror. 1

At the receiving station, the light is caught by the lens II andconcentrated upon the lens I l where it is made parallel and enters thebody I! normally to the face II. Within the body I! the light is totallyreflected' because, whenever it becomes incident upon the surface, theangle of incidents is larger than the critical angle, and, afterrepeated reflections if necessary. it arrives at the edge ll normally ornearly normally to the surface there. The light emerges from the edge II but will not emerge through the cylindrical surface or through theflat surfaces i! and II.

The sheet ll rotates with the body l2. When this sheet, acting as ananalyzer, is in the position of optical coincidence with the plane ofpolariration of the arriving light, it permits the passage of light mosteffectively, but when it is in a position at right angles thereto, itwill cut oil the light. If, the sheet is of suflicient thickness, thiscutting off of the light at a particular position is complete, althoughin a position at right angles thereto, the sheet offers but littleobstruction the passage of light.

There will be, therefore, a position of the body .I! and the screen I inwhich little or no light will emerge from the edge II. II and analyzerII are in a position at right angles to this, a maximum amount of lightwill emerge from the edge ll.

The rotation of the body I! and the analyzer is at such a speed that theedge II returns to any [given position before the visual impression,created when it was formerly in that position, has faded. In otherwords, the speed of rotation is .greater than the persistence of vision.It is a consequence of these actions that there appears to be a brightarea in the central part of the ring 24, but the light in this area isnot uniform. In-

.stead, there will be one direction across it where little or no lightfrom the edge I6 is received and another band at right angles thereto atwhich the received light is a maximum.

If the observer looks at the ring II from the side opposite the body I!he will see this distribution of light in the open space at the middleof the ring. If the field of light delivered by the rotating edge II iscrossed by a material surface,

- of ring 24 indicated on either core butalways the surface must beclose or convenient to the edge II for accuracy.

when the body The change with its rotation of light transby the placescorresponding to the highest pointof this curve. The dark line acrosstheilluminated area will, therefore, be more sharply marked than theline of greatest illumination. For this reason the dark line will servebetter as a pointer and the indicia placed upon the ring 24 cooperatewith thistdark line to give to the observer the information intended.

In the application of the invention chosen for illustration, theinformation conveyed is the direction of the lighthouse or other sendingstation from the receiving apparatus. Thus in the situation illustratedin Fig. 6 the sending station is west-north-west from the receivingstation.

10 The same position of the pointer could very well mean that thesending station is east-southeast from the receiving station. Theoperator receiving the signal usually knows enough about his positionfrom other sources of information to distinguish properly between thetwo possible meanings. Ships approaching a harbor entrance or airplanesapproaching a landing field ordinarily know approximately theirdirection of approach but desire some such signal as is here proposed tolearn'the exact bearing.

If desired, the polarizer instead'of being located in the frame 2, Fig.1, maybe located in the path of the horizontal beam and rotated bysuitable gearing, meshing for example with worm. wheel 2 5, whereby anyone position of the mirror 8 is associated with a definite position ofthe polarizer.

In addition there may be, if desired, provision for neously controlled,the direction of the plane of polarization being selected at will foreach of the beams.

Three separate sources of light, two of which are shown in Fig. 8 at Iiand 32 are provided for supplying the three beams of light. Each light4;) source is surrounded by a parabolic mirror. As-

. sociated with each light source is a color screen. Two of thesescreens are shown at 33 and 34 respectively in Fig. 8; the third one,being behind screen 33, does not show, each light source also hasassociated with it a sheet of polarizing material. Two of these, IIand", appear in Figs. -'l and 8, the third one, 81, appearing only inFig. 7. Means are provided for rotating the three polarizers l5, l8 and31 at will. In the form illustrated, the common driving means is amanually operated handle 88. mounted upon a pivot 89 as close'to thecenter of theassembly of light sources and polarizers as can beconveniently managed. The lever 38 is equipped with three finger piecesll, 42 and 43. each equipped with a plungerto operate a bellcrank-lever. three of which are shown in Fig. 8. Each of these bellcranklevers is connected to a link, the link M, associated with the fingerpiece 43, being most 00 clearly shown in Fig. 8. E ch link is connectedto a lever, one of which, 4 is clearly shown in Fig. 8 and all three ofwhich are shown in, end

' which it may slide. One face of the boss acts as. a seat againstwhichsprings, one for each plunger, bear; the other ends of the springsbearing on the respective levers, like 45. Thejsprings bias the partstoward the illustrated positions, in which the plungers, like 40, aretoward the left and the flngerpieces are spaced away from the handle 38.

Three rings l0, ii and "are mounted to re- CROSS RtttlitNUl:

volve about the center of the assembly of light sources and polarizers.Each of these rings is rovided with a" toothed section. extending oversomewhat more than 90, best shown at 53 in Fig.

7. The three rings are so positioned that their respective toothedsections are opposite the three plungers, like 46.

Each of the rings is provided with a depending finger. The finger 54,integral with the ring 50, is

shaped to extend around the edges of the other rings and extends into aslotted lug 55 upon the frame of the analyzer". A pointer 56 extendsfrom this lug into juxtaposition with a scale 51 cooperates with thepointer to prevent rotation of the polarizer beyond a useful amount. Thering 52 has a similar finger shown at 83 in Fig. 7 for cocperating withthe analyzer 31.

The three light .beams from the three light sources are caused to uniteinto a single light beam by a body 65 of fused quartz or similar material having at one end a three-part division into cylindricalportions, two of which 86 and 61, show in' Fig. 8. The end surfaces of'the three portions lie opposite the three respective light sources andhave flat ends, whereby the light from the three sources may enter thethree cylindrical portions. These cylindrical portions merge into a maindelivery portion 68 and emerge at the further end WHlliu-n thereofthrough'a' similar flat end surface. If

preferred, the merging of the three light beams may be accomplished byhollow metallic reflecting members. 3

The receiving apparatus to be used with the sending apparatus shown inFigs. 7 and 8 includes Opposite the ends 1 I, 12 and the third end, not

shown in the drawings, are located color screens I8, 14 and one notshown, which are of the same color as the screens 33. 84 and the one notshown in Fig. 8. Opposite each color screen is an analyzer, II, 16 andone not shown, which are of polarizing material such as herapathite. Thethree analyzers are preferably attached respectively to three quartzbodies shaped like the body I! in Figs. 4 and 5. These bodies are shownat 11, I8 and 18. Each is mounted in a ring equipped with a crown gear.two of which show at and 8!, but the third does not show in Fig. 9.

The three edges of these bodies are illustrated as occupying differentangular positions in a plane parallel to the end surface 10; The threeoptical bodies together with their analyzers are intended to becontinuously rotated. This may be done by any suitable common drivingmeans meshing with the'three crown gears. two of which are illustratedon the rings 80 and II.

- Opposite each of the three rotating quart bodies is a photocell, twoof which are shown at 82 and 88. One of these photocells is illustratedin detail in Figs. 10, i1, and 13. Each photocell comprisesa'n envelope85 within which is mounted nected by a conductor ll as shown in Fig.11

- and the other two by a conductor".

' The conductors 88 and II are respectively connected to oppositte endsa resistor Ill. The

- l central point of this resistor is connected to the negative end of abattery ii, the positive end of which is connected to the anode througha' lead shown at It. The midpoint oi the battery II is connected to thecathodes of two vacuum tubes 2 diflcally illustrated at It and 04. Thegrids of the tubes are connected rmpectively to the two ends of theresistor 00 and the plates are connected to two difierent field-windingsII and II which cooperate with the rotor ll of a motor I". The junctionof the two fields is connected to the positive terminal of a B-batteryII. The negative terminal of this battery like the midpoint oi thebattery I is connected to the cathodes oi the tubes.

The operator at the sending station shown in Figs. 7 and 8 manipulatesthe three polarisers It, ii and I! by ineans oi the handle ll. To dothis he grasps the handle, depressing as he grasps it one or more oi thefinger pieces", 42

3 and 43, depending aipon which or the polarisers he intends to move.The plungers like 0 connected to the depressed finger piece move intoengagement with the toothed section on the corresponding rings like. II.Then I the operator moves the handle so and the rings which have beenclutched thereto are'moved. The springs acting on the plungers like Itaccommodate them to the eccentric mounting oi handle 38 relative to therings like ll. The rings which are moved,

4 move the corresponding analyzers through fingers like It and slottedlugs like it. Pointers like to are moved at the same time and enable theoperator, by observing the position or the pointers, relativeto thescales like II to know in what position he has placed each of thepolarisers.

The stops at the ends of the scales prevent rotation of .any onepolariser through much more than an angle of 90. Useless movement of thepolarisers and confusion between two equivalent positions thereof 8thereby avoided.

Light iromthe three senroa. 8i, )2 and the one not shown. produces threebeams oi'calored light. Preferably the colors are so chosen that,

when combined, they will produce white light 00 Red, green and yellowmight, for example. be the colors chosen for the three color screens. Ineach beam theccolored light passes through a polarizer and, therefore,enters the cylindrical part, it, 61 or the one not represented in Fig.

6 8, as pane polarized light.

The three beams are polarized in planes which have'an arbitrary relationto one another, the planes having been'fixed by the action of theoperator in rotating the polarizers ll, It and 7 31 in accordance withthe signal he wishes tq convey. The three beams coalesce by the mergingaction of the optical body 85' and emerge irom the single end oi thisbody as a beam of white light.

75 No person imacquointed with the way in whichingtheappearaneeoithebeameitherthatitcontainedsignalsorhowtbesignalswere conveyed. and no one without areceiving device desianedior this'lm v l could mm the lilnals.

I The receiving device is illustrated in Pig. 0. light from the sendingstation impinges on the fiat end I. o! the quartz body and is dividedinto three beams by the action of this body. Each beam is received upona color screen It, It and one not repre'sented. Only light 0! the colorcorresponding to the screens a, l4 and theone in Fig. 8 not represented,will emerge from the color screens at the receiving station. The li htis thus divided at the receiving station into three colored parts, eachof which is polarised in a planefixed bythe polariser associated withthe color'screen oi the same color at the sending station.

The three rotating wedge-shaped bodies I1, 18 and ll producethree-circular fields or light in the way ducribed in connection withthe one wedge-shaped body and the one illuminated field shown in Figs.4, 5 and 6. The three illuminated fields will be of three difierentcolors. The black line crossing any one oi these fields will be in aposition fixed by the operator at the sending station when he positionedthe oorruponding polariser II, It or 31.

The operator at the sending station is. there- 'iore, able to produce atthe receiving stationthree signals, each indicated by the position of ablack line on an illuminated field. By suit-, ably chosen combinationsof these three indications a very complete andelaborate communthroughthe other pair and there will no potential diilerence between the twoends -otthe resistor Ill. There will, therefore, be no tendency torotate the armature OI.

It the polariser at the sending station is rotated away from theposition corresponding to the position of the black line I" justdiscussed, the blacklinewillrotate. Onepairoi'cathodeswill to rig. 12,wherein the plates 81 are shownina developed relation and the curve IIIis located with the crestsoppositethegapsbetweentwoplatesand the troughsopposite the other ga 11 the illumination o! the plates is rota theelect upon its relation to the plates s1 can be shown.

by indicating difierent positions for these gaps,whichhasbeendoneinl'lg.12bydottedlhses pairs of cathodes. The currentthrough one pair of cathodes -.will then be equal to the t I02. Theseindicate the position of the gaps relative to the curve when the curvehas moved to the right. 'I'he curve III is related to the lines i 02 ina way to show the relation of the illumina- 5 tlon to the gaps betweenthe cathode 81 when the dark line I has been rotated through a smallangle.

It will be apparent from a study of these lines and the gaps. There isalso an addition to the light on left-hand plate I! and on the thirdplate 20 81 from the left represented by the same small areas. Thechanges in illumination of the plates 81 occurring at the troughs of thecurve are small .compared with the changes represented by the shadedareas. The result, therefore, is that v 25 one pair of plates 81 nowreceive less light and the other pair receive more light.

The rotation of the armature 91 will now occur and may be employed tomove a pointer which the attendant at the receiving station might be re-30 quired to observe. It may likewise be employed to move a recordmaking device so that a written record of the signal could be made atthe receiving station. It might also be employed to rotate the photocellitself as is illustrated in Fig. 13 and thereby maintain it in aposition where the black line crosses it between two cathodes.

With the latter operation, the armature 91 would be'energized only whenthe attendant at the sending station is in the act of moving the 40polarizers.

set up a permanent indication at the receiving station of the positionselected at the sending station, even when the light sources areextinguished soon after the positions were estab- 45 lished.

If the light from the optical body 65 is too scattering to convey asignal to any great distance, a more parallel beam can be obtained bytapering the end 68 to a small and surface or a point and 50 locating itat the focus of a beam-forming optical system, for example, a parabolicmirror or a lens. Although the description has been written in terms ofvisible light, it will be apparent to those skilled in the art thatinfra red or ultra violet 55 light could be employed effectively. Thebeam of light would then be unobserved by persons not concerned in thesending or receiving of signals and the signaling can thus be made'completely secret.

If, on the other hand, visible light shouldbe employed, it would appearto those not acquainted with the transactions that it was a steady beamof white light and they would have no means of knowing when it wasmerely a 85 beacon light and when it was communicating signals. Noindication of the action of signaling would be apparent to any oneexcept an observer equipped with thereceiving apparatus describedherein. when used to convey signals to an airplane, the means for movingthe several polarlzers may advantageously include a lever resembling thecontrol stick of the airplane. may be used to move the three polarizersin lo accordance with the three components of the It would, therefore,be possible to Suitable gearing motion of the stick and three motorslike the 'armature 91 of Fig. 11 may move a pointer or pointers on theairplane or may move the controls themselves of the airplane without theintervention of a pilot.

Although colors are discussed in connection with Figs. 7 to 9, it is notintended to indicatethat monochromatic light is necessary in Figs. 1 to6. If white light is used, the color fingers produced are too small tointerfere with the designation of proper signals.

Many other modifications in details and many modifications of thesystemproposed will occur to those skilled in the art. The specificillustration and description are only a few of the possible formsof thisinvention. It is not to be construed as a limitation.

I claim as my invention:

1. In an optical signaling system, a light source,

means for producing a beam of plane polarized. light therefrom, meansfor rotating the plane of polarization of said beam, while preservingthe character of the light as plane polarized light, in

accordance with the signal to be sent, a continuously rotating analyzerin the path-of said beam and means cooperating with said analyzer toindicate the signal.

2. In an optical signaling system for transmitting and receivingcorrelated signals, a light source, means for producing therefrom aplurality of beams of polarized light of mutually distinguishingcharacteristics to correspond to each of said signals, means forseparately rotating the plane of polarization of each of said beams inaccordance with the respective signals, continuously rotating analyzers,one for each beam, and means cooperating with each analyzer to indicatethe respective signals.

3. In an optical signaling system for transmitting and receivingcorrelated signals, one or more light sources, means for producingtherefrom a plurality of beams of polarized light each beam being of adifferent color to correspond to each of said signals, means forseparately rotating the plane of polarization of each beam inaccordsignals conveyed by the respective beams.

4. In an optical signaling system for transmitting and receivingcorrelated signals, one or more light sources, means for producingtherefrom a plurality of beams of polarized light each beam being of adiiferent color to correspond to each of said signals, means forselecting any number of said beams and rotating the plane ofpolarization of each of the selected beams through individuallydetermined angles in accordance with the several signals to be conveyedthereby, continuously rotating analyzers, one for each beam, colorscreens for shielding each analyzer from all but its respective beamandmeans cooperating with said analyzers for indicating the signalsconveyed by the respective beams.

5. In combination, an analyzer for polarized light, alight-concentrating device positioned to receive light from saidanalyzer, said device having a substantially linear light-deliverysurface, means for rotating said analyzer and device at a speed abovethe persistence of vision and a reference scale cooperating with thedelivered light to indicate the azimuth of the polarization.

6. In combination, an analyzer for polarized light, alight-concentrating'device positioned to receive light from saidanalyzer, said device having a substantially linear light-deliverysurface, means for rotating said analyzer and device at s a speed above.the persistence of vision, a screen receiving light from said device,and an indicating scale adjacent said screen.

7. In a receiving device for polarized light,

field of illumination of .an intensity varying withs the phase of saidrotation is produced.

8. In a receivingdevice for polarized light, an analyzer, optical meansfor concentrating the light delivered by the SIIBJYZBTJIEO a beam ofapproximately linear cross section, means for ro- -z tating saidanalyzer, whereby the light delivered 9. Incombination, means forsending light polarized in a selected plane, an analyzer in po- 3 sitionto receive light from said means, means cooperating with said analyzerto produce a fielddistribution of illumination the intensitydistribution in space of which is correlated to the selection of theplane of polarization and translating means for giving significance tosaid distribution. 10. In combination, means for sending light polarizedin a selected plane, an analyzer in position to receive light from saidmeans, means cooperating with said analyzer to produce a sur-- 0face-distribution of illumination the intensity distribution in space ofwhich is correlated to the selection of the plane of polarization and aphotocell having light-sensiti've elements so positioned relative tosaid illumination that changes in said 45 distribution will alter theoutput of said photocell.

11. In combination, means for sending light polarized in a selectedplane, an analyzer in position to receive light from said means, meanscooperating with said analyzer to produce a fielddistribution of lightcorrelated to'the selection of the plane of polarization, a movableobject and means responsive to changes in said distribution for movingsaid object into a position corresponding to the selected plane.

12. In a light-translating system, a photoresponsive device havinglight-sensitive elements symmetrically arranged in pairs, unitary meansresponsive to the distribution of illumination over said elements forindicating when the li- Go lumination of one symmetrically situated pairof elements differs from the illumination of another such pair.

18. In a light-translating system, a photoresponsive device havinglight-sensitive elements symmetrically arranged in pairs. meansresponsive to the distribution of illumination over said elements forindicating when the illumination of one symmetrically situated pair ofelements differs from the illumination of another such pair. meanscontrolled by said response i'orunoving the photo-responsive deviceabout the center of said symmetry, the sense of said movement beingdetermined by the sense of said diiference of illumination.

14. In combination with a means for producing a distribution ofillumination symmetrical about an axis of symmetry, a photo-responsivedevice having light-sensitive elements symmetrically arranged about acenter of symmetry in said axis of symmetry means controlled by anydifference in the total illumination of the elements on one side of saidaxis from the total illumination of those on the other sidefor sorotating the photo-responsive devices that equality of --said totalswill be restored, whereby rotation of the distribution of illuminationwill be initiated by rotation of the photo-responsive device.

15. In a receivingdevice for polarized light, an analyzer, optical meansfor concentrating the light delivered by the analyzer into a. beam ofapproximately linear cross section, means for rotating said analyzer,whereby the light delivered therefrom will vary in intensity, said meansalso rotating said optical means to cause said beam of concentratedlight to rotate synchronously with said variation in intensity, alight-receiving surface in position to be illuminated by said rotatingbeam and means cooperating with said illuminated surface to produceindications from changes in distribution of the illumination thereon.

16. In a system for indicating the position of an element, means forproducing a beam of polarized radiations, means for so swinging saidbeam that it generates a surface including the region in which saidelement lies and simultaneously rotating the plane of polarizationofsaid radiations in such manner that the angular position of said beam isa function of the angle of rotation of the plane of polarization andmeans associated with said element and responsive to said beam inaccordance with its plane of polarization for indicating the angularposition of said beam.

17. In a system for indicating the position of an element, means forproducing a beam of polarized radiations, means for so swinging saidbeam that it generates a surface including the region in which saidelement lies and simultaneously rotating the plane of polarization ofsaid radiations in such manner that the angular position of said beam isa function of the angle of rotation of the plane of polarization, meansincluding a continuously rotating opticalanalyzer disposed in the pathof said beam and means for indicating the plane of polarization of thebeam transmitted through said analyzer for indicating the angularposition of said beam.

18. In a system for indicating the position of an element, meansfor-producing a' beam of polarized radiations, means for so swingingsaid beam that it generates a surface including the region in which saidelement lies and simultaneously rotating the plane of polarization ofsaid radiations in such manner that the angular position of said beam isa function of the angle of rotation-of the plane of polarization andmeans associated with said element for indicating the plane ofpolarization of said beam.

' LEWIB'W. CHUBB.

